The present invention relates to control of foodstuff or perishable products conservation.
In particular, the present invention relates to a device for detecting thawing of frozen or deep frozen foodstuff, i.e. device that indicates that the outer surface of these products has accidentally reached a temperature higher than the thawing temperature, precisely measures duration of this thawing condition and signals the expiration of the period, during which the product organoleptic features remain unchanged.
It is known the necessary of maintaining the continuity of so-called xe2x80x9cfreeze chainxe2x80x9d from the foodstuff freezing until its consumption to guarantee the product nutrient, organoleptic and hygienic integrity.
This means that, during the whole conservation period, the products cannot undergo even partial thawing and refreezing.
In fact, interruption of the freeze chain deteriorates foodstuff, causing a considerable decrease of the nutritional value or creating true toxins or proliferation of bacterial colonies.
In each case, consumption of deteriorated products is to be discouraged and moreover, the law forbids sale of deteriorated products.
However, only in some cases and for some products it is possible to detect a momentary thawing and subsequent refreezing.
Empirical signs are e.g. the presence of a layer of ice or frost on the package, certain degree of humidity of the carton package, or scarce rigidity of the touched product. However, these signs cannot give a reliable indication about possibility that the products have undergone a freeze-thaw sequence.
A known technique for detecting that the continuity of the freeze chain in the foodstuff was interrupted, has been described in the Patent Application No. MI92A 000526, filed by the same Applicant.
The above mentioned invention includes a tag, which undergoes irreversible chromatic changes as a result of the contact with liquid water.
The tag can be applied to the inner surface of the transparent cap of a small container filled with a gelatinous aqueous substance, which solidifies in the normal freezing temperature of the preserved product, and with a temperature near to zero grades, it melts and releases liquid water.
The container is usually frozen and then applied to the product also frozen, so the gelatinous substance contained therein is solid.
If in any moment the temperature of the container gets near to zero, the substance contained therein thaws and releases liquid water which wets the tag.
This leads to an irreversible chemical reaction causing the tag color change, which is seen from the outside through the transparent cap.
The above mentioned Patent Application describes different types of substances which react in different chromatic ways with water, and therefore can be advantageously used in this device e.g. by being silk-screen printed or painted on the tag.
Moreover, according to the above mentioned invention, the tag is covered also with surface-active agents or organic solvents.
The above described invention is able to give sufficiently precise information about possible thawing, yet, it is not able to give information about duration of the partial or complete thawing condition.
This information can be very important for a trader or the user, since it allows to understand if either the package only or the package and the product have been subjected to thawing, and if the product characteristics have been changed to such degree as to advise against its consumption.
The European Patent Application No. 003.126 describes a thawing indicator constituted by a strip of absorbent paper provided with a water-soluble substance, which changes color when in contact with liquid water.
This strip is wrapped in a transparent and impermeable film, except for a piece thereof which is situated on one of its ends.
The indicator is applied to the frozen product and absorbs, by its free piece, the water released during the product thawing, if the temperature goes over 0xc2x0 C.
The gradual color change of the substance contained in the absorbent paper strip indicates approximately the duration of the thaw at the product surface.
A disadvantage of this indicator lies in the fact that the components used and the construction method make the absorbent paper absorb the water rather quickly and thus the indicator reaches the end of scale rapidly.
Moreover, the speed of water expansion in the paper is proportional to the reached temperature, and anyway it is difficult to verify.
This can lead a possible purchaser to negative opinions about the product state also in situations when only the package or the outer layer of frost has undergone thawing and therefore, the product is still absolutely edible.
For example, this occurs normally during wrapping of the product, when the product is put onto a polystyrene tray and then wrapped in a thin impermeable film or during packaging in heat-retractable bags.
In both packaging ways, the packages are heated for a short instance to a temperature near 100xc2x0 C., which causes immediate thawing of the frost present on the product outer surface, thus activating the above described indicator.
A further known temperature monitor device is disclosed in U.S. Pat. No. 3,243,303. It comprises an absorbent layer, a masking layer overlaying the absorbent layer, an impermeable layer underlying this latter except for end areas, a fluid carrier underlying the impermeable layer and two external transparent layers, enclosing and sealing the device.
The fluid carrier is impregnated with a fluid, containing coloring matter, normally held in a frozen status. When temperature raises above 0xc2x0 C., the fluid melts or thaws, and is adsorbed by the adsorbent layer, traveling from the end areas to the indicating area and coloring it.
The above device must be constantly held at temperatures under the internal fluid melting temperature, even before its installation in a frozen product.
As a matter of fact, the indicators of this type have not been very successful and have practically disappeared from the market, probably due to the above described disadvantages.
The object of the present invention is to propose a device which not only detects even minimum thawing in a frozen or deep frozen product, but also visibly signals it in a clear way only when the thaw condition has lasted long enough to make the product not advisable to be sold or used.
Another object of the present invention is to obtain the above mentioned objects by a very cheap and highly reliable device of simple construction and application.
The above mentioned objects are achieved, in accordance with the content of the claims, by a device for detecting, assessing and signaling thawing of deep frozen foodstuff, the device being applied to an area of the product to be checked where liquid water is released during thawing, the device including:
a first support, made of laminar, scarcely permeable material, and having, situated in a lower surface, a pattern extending from an outer edge zone of said first support up to a display zone thereof, said pattern being formed by substances for facilitating water expansion through said pattern and coloring water-soluble substances applied in said display zone;
impermeable transparent films, upper and lower respectively, whose shape is identical to said first support, said upper and lower transparent films being fastened to an upper surface and to a lower surface of said first support, so as to allow water to expand only in said outer edge zone.
According to a different embodiment, the invention proposes a device for detecting, assessing and signaling thawing of deep frozen foodstuff, which includes:
a first support, made of laminar, scarcely permeable material, and having applied to a lower surface and in a display zone, substances facilitating water expansion through said display zone and also coloring water-soluble substances;
impermeable transparent films, upper and lower respectively, whose shape is the same as said first support, said upper and lower impermeable transparent films being fastened to an upper surface and to said lower surface of said first support, said lower film having a hole made in said display zone;
a predetermined quantity of gelatinous adhesive substance, containing water, applied in the region of said hole for fastening said device to a package of frozen products.